The present invention relates to an electronic distance measuring instrument which receives a reflected light from an object to be measured and performs a distance measurement.
A surveying instrument such as a laser scanner or a total station, or the like has an electronic distance measuring instrument which detects a distance to an object to be measured by a prism distance measurement using a reflection prism or by a non-prism distance measurement using no reflection prism.
An optical system used in the electronic distance measuring instrument is required to be capable of performing a sighting at a high magnification and a high resolution. For this reason, an aperture of a lens (or a lens group) constructing the optical system is a large aperture and a long focal length. For this reason, the optical system is large in size and heavy.
The electronic distance measuring instrument has a lens group constructed of plural lenses, and an incident light is arranged to focus on a light receiving surface by a refraction action of the lenses. The lens group has a focal length f, and this focal length is determined by a performance required for the optical system in the electronic distance measuring instrument.
Therefore, a light receiving unit in the electronic distance measuring instrument must have a size adequate to accommodate the lens group, and a length of an optical axis direction is dependent on the focal length f. Further, in recent years, a miniaturization and a weight reduction of the electronic distance measuring instrument are achieved, but regarding the optical system, it is still difficult to miniaturize due to a restriction on a size of the lens group and the focal length f.